A conventional hearing aid of this type comprises a body case that is worn behind an ear, and a string-shaped sound conductor that is linked at one end to this body case and at the other end to an earpiece, and there is a known example in which a string-shaped engaging part that engages with the antitragus of the ear is attached to the other end of the sound conductor (see Patent Literature 1, for example). With this hearing aid, the body case is worn behind an ear, and the earpiece is inserted into the external auditory canal, after which the engaging part is engaged with the antitragus of the ear, which keeps the earpiece from coming out of the external auditory canal.
With the above hearing aid, the string-shaped engaging part is designed to be longer because the size of an ear varies with the individual wearing the hearing aid. Therefore, when a person with small ears wears the hearing aid, the distal end side of the engaging part is cut off with scissors or another such cutting tool to adjust the length. In other words, the engaging part has to be cut with the above-mentioned cutting tool in order to match it to the size of the ear of the individual wearing the hearing aid, and this made the fitting of the hearing aid more difficult.
In view of this, it has been proposed that a ring-shaped engaging part that engages with the tragus be attached to the other end of the sound conductor of the hearing aid (see Patent Literature 2, for example). With this hearing aid, one end of a string-shaped engaging part is linked to the other end to form a ring, and the size of this ring can be varied by retracting or extending the other end. This constitution can accommodate differences in the size of the ears of the individuals wearing the hearing aid.